PROTOZOA 229 



515. The Ciliata are classified on the basis of the arrangement of the 

 cilia. The Holotricha have no special zone of cilia in the region of the 

 mouth. The Heterotricha have a left-hand spiral of larger cilia around the 

 mouth. The Oligotricha have a spiral or circle of cilia around the peri- 

 stome which is anterior and at right angles to the axis of the body. Else- 

 where the body is almost or wholly destitute of cilia. The Eypotricha are 

 flattened dorso-ventrally. The adoral spiral is on the ventral side and the 

 dorsal side is without motile cilia. The Peritricha have the adoral spiral 

 right-handed, otherwise the body is not ciliated, many are stalked and 

 colonial. 



FIG. 128. Paramcecium. A, Anterior; c, cilia; e.c., ectoplasm; e.n., endo- 

 plasm; f.v., food vacuole; g, gullet; N, macronucleus; n, micro nucleus; o, oral 

 groove; p.v., contractile vacuole; tr, trichocysts; v, food vacuole. 



516. Class V. Suctoria. In this group there are no organs 

 of locomotion in the adult and consequently all are sessile or 

 at least motionless. They are provided with long tubular pro- 

 cesses by which they catch their prey. Through these tubes 

 they then suck the protoplasm of the small animals they have 

 caught. The young are formed by budding. They are 

 provided with cilia by which they swim about for a time before 

 becoming attached. Some suctoria are parasitic. The group 

 is not large and is comparatively unimportant. 



Metazoa 



517. The Metazoa are multicellular animals. In the embryo the cells 

 are arranged in three distinct layers, an outer ectoderm, an kiner entoderm 



